Traumatic brain injury (TBI) is one of the leading causes of death and disability in the United States with a very conservative estimate of 1.7 million people affected annually and no less than 5 million people currently suffer from TBI sequelae. After the initial trauma in the central nervous system (CNS), secondary injury (e.g. hypoxia, inflammation, etc.) mediates tissue damage and the deposition of extra-cellular matrix (ECM) molecules leaves scars that inhibit normal tissue repair and full functional recovery. ECM deposition in acute CNS injury consists of the extensively studied glial scar and the relatively newly recognised CNS fibrotic scar. The mechanisms of these events following TBI are poorly understood and the CDC and NIH have encouraged researchers to elucidate them. Previous works in micro-RNAs (miRNAs) has shown that downregulation of miR29b and upregulation of miR21 are vital for ECM deposition after injury and give us a novel way of investigating potential interventions to change outcomes after TBI. We propose to manipulate these miRNA levels to not only clarify the mechanism of fibrotic and gliotic changes after TBI but also to potentially improve recovery after injury by attenuating ECM deposition. Furthermore, YAP, a co-transcription factor and member of the Hippo signalling pathway, has been recently found to contribute to fibrosis in the liver and kidneys and is an important modulator of miRNA levels. Therefore, in this proposal, we will study miR29b, miR21 and YAP in tandem. We have shown that miR29b decreases and miR21 increases simultaneously after TBI and that this correlates with fibrosis and gliosis in the lesion area. This proposal will test the hypothesis that increasing miR29b and decreasing miR21 levels will improve TBI recovery from decreased ECM deposition. In the first specific aim, we will investigate our preliminary findings that miR29b and miR21 will decrease and increase, respectively, after TBI, and that these levels correlate with their target genes (specifically ones involved in ECM deposition such as chondroitin sulphate proteoglycans, collagen1a1, etc.) in neurons, astrocytes, microglia and perivascular fibroblasts. As miR29b decreases due to TGF? and other inflammatory cytokines suppressing its transcription, miR29b derepresses its pro-fibrotic target genes and promotes fibrosis. As miR21 increases after injury, its targets (PTEN, PPAR?, Smad7, etc.) will decrease and that has been shown to also promote fibrosis (and gliosis after spinal cord injury). In the second aim, we will investigate the causal link among miRNAs, YAP and their gliotic and fibrotic specific target genes in two prototypical cell types for ECM deposition in the CNS: astrocytes and fibroblasts. We will validate our viral method for manipulating the miRNA levels, downstream mRNA and protein levels of the pro- fibrotic and gliotic miRNA target genes. This will lead to our third and final aim to see if manipulating the miRNA levels (with or without YAP changes) will improve the anatomic and behavioural recovery following TBI via attenuated gliosis, fibrosis and ECM deposition. These proposed studies will help define the contributions of miR29b and miR21 in fibrosis and gliosis in TBI and, potentially give new venues to pursue clinical therapeutics.